Brand index was a feature some Pentium III and Pentium 4 CPUs.
It provided an index into a software lookup table to provide a
brand name for the CPU. This is separate from the family/model.
It's unclear to me why this index being non-zero was used to
block checking family/model. None of the CPUs that had a non-zero
brand index are supported by __builtin_cpu_is or target
multi-versioning so this should have no real effect.
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